Nanoparticles used in cosmetics and sunscreens pose no human health risk, and even help improve health by protecting consumers against skin cancer, according to a recent report. In a review of the available toxicity data on nanoparticles used in cosmetics and sunscreens, scientists at L'Oreal in collaboration with researchers at the University of Queensland, Australia, have concluded that they do not pose a health hazard.

This conclusion is in contrast to a number of recent campaigns arguing that nanoparticles may have as yet undocumented effects on human health and should be avoided.

Published in Skin Pharmacology and Physiology, the report investigates the penetration of nanoparticles such as TiO2 and ZnO into the deeper skin layers-the epidermis and dermis. It also looked into their potential for toxicity. The study concludes that the benefit provided in terms of UV protection greatly outweighs any 'unproven and hypothetical risks'.

Skin penetration of nanoparticles

The results of a number of skin penetration studies on titanium dioxide TiO2, a popular sunscreen agent whose efficacy is dependent on a particle size of 60-120nm, suggest that micro- and nano-sized particles remain on the skin surface and do not penetrate into the living skin layers, according to the report.

Absence of penetration of even smaller nanosized particles-20nm size TiO2-was also confirmed by the EU NANODERM research group, added the scientists led by Dr. G. J. Nohynek from L'Oreal.

TiO2 particles have been found in the hair follicles however, which has been interpreted by some to mean penetration into the living skin. However the particles remained outside the dermis and epidermis, noted the team, who maintain that this does not show penetration into the living skin.

Furthermore, recent data from mice skin studies illustrates that even when TiO2 nanoparticles were injected under the skin, they remained at the injection site and did not migrate.

The scientists therefore conclude that the fear that nanoparticles can penetrate the skin, get access to the lymphatic system and circulate around the organism is 'simplistic and physiologically improbable'.

Toxicity not generally dependent on size

Nohynek and the team proceeded to look at the data regarding the effect that particle size may have on toxicity.

"No major difference in the safety profile was observed for micro- and nano- sized particles, and no evidence was found suggesting that nano-sized particles pose greater or qualitatively new hazards," they concluded.

In addition, they note that a significant number of studies that suggest nanosize-specific effects suffered from a fatal flaw in that they did not test the nanosize particle against a control of a larger particle of the same material.

Although the report recognizes the impossibility of disproving all hypothetic risks, it concludes that, "The current weight of evidence suggests that nanomaterials currently used in cosmetics preparations or sunscreens pose no risk to human skin or human health; on the contrary they provide a large benefit to human health by protecting human skin against the adverse effects of UV radiation."